Among the following, the maximum covalent character is shown by the compound:

Correct answer: (a) AlCl₃

Explanation

By Fajans' rules, an ionic bond takes on covalent character when a cation distorts (polarises) the electron cloud of the anion. A cation polarises more when it is small and highly charged.

Al³⁺ has a +3 charge and a very small size, so it polarises the chloride ion strongly, and AlCl₃ is largely covalent: it sublimes easily and exists as Al₂Cl₆ molecules. Mg²⁺, Sn²⁺ and Fe²⁺ carry only a +2 charge and polarise the chloride ion less.